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Mesoscopic Interference of Rotated Spins in Graphene Coupled to High-Spin–Orbit-Coupling Substrates
(2025-11-05)
Yokoi, Kazushi
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Somphonsane, Ratchanok
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Ramamoorthy, Harihara
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Arabchigavkani, Nargess
;
He, Keke
We explore the manifestations of spin rotation in graphene in proximity with two different types of high-spin–orbit-coupling (SOC) materials (ferromagnetic Co and nominally diamagnetic WSe<inf>2</inf>). Using weak antilocalization (WAL) as a probe of the induced rotation, we demonstrate that spin interference exhibits a highly stochastic (nonself-averaging) character in the mesoscopic limit. At low temperatures (<20 K), the spin rotation is manifested as a zero-bias peak (or zero-bias anomaly, ZBA) in the differential conductance, a feature that, as expected for WAL, is suppressed by fairly modest magnetic fields (<∼102mT). The ZBA moreover exhibits a stochastic variation when a gate voltage is used to sweep the Fermi level through the graphene bands, with ranges for which the antilocalization is either prominent or strongly suppressed. This mesoscopic character is exhibited by both of the studied systems, whose ZBA is also damped in similar fashion with increasing temperature. We thus provide fundamental insight into the nonensemble-averaged (nonself-averaged) character of spin interference in mesoscopic systems with strong SOC and, more specifically, into how the details of spin rotation are impacted by external gating. This understanding may ultimately enable the efficient modulation of spin currents in future spintronic devices.
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Alkanolamine-Grafted and Copper-Doped Titanium Dioxide Nanosheets-Graphene Composite Heterostructure for CO2 Photoreduction
(2023-11-13)
Karawek, Apisit
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Kitjanukit, Nutkamol
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Neamsung, Wannisa
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Kinkaew, Chonlathon
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Phadungbut, Poomiwat
CO<inf>2</inf> photoreduction is an intriguing approach to carbon capture, utilization, and storage (CCUS). It relies on an effective photocatalyst to generate photoinduced electrons that incorporate carbon dioxide (CO<inf>2</inf>), yielding fuel products, e.g., methane, methanol, and ethanol. The heterostructure of titanium dioxide nanosheets (TNS) and graphene oxide (GO) is a sandwich-type composite consisting of two 2-dimensional nanostructures (2D-2D). It was demonstrated as an excellent candidate for CO<inf>2</inf> photoreduction due to its outstanding charge separation ability. This research studied the photoactivity of alkanolamine-grafted TNS and alkanolamine-grafted and copper-doped TNS/GO composites. In the first experiment, triethanolamine-grafted TNS (TEA-TNS) exhibited the best ability in CO<inf>2</inf> photoreduction compared to monoethanolamine- and diethanolamine-grafted TNS (MEA-TNS and DEA-TNS) due to the base-catalyzed hydration nature of CO<inf>2</inf>-TEA interactions. In the second experiment, we studied the photoactivity of four composites, including copper-doped TNS/GO (Cu-TNS/GO), TEA-[Cu-TNS/GO] (grafting TEA on Cu-TNS/GO), Cu-[TEA-TNS]/GO (doping Cu on TEA-TNS/GO), and TEA-Cu-TNS/GO (one-step hydrothermal synthesis with the Cu precursor, TEA, and GO). TEA-[Cu-TNS/GO] showed the best photoactivity since TEA was added last to the heterostructures, which benefited in avoiding side chelation reactions between TEA and Cu ions and ensuring TEA exposure to CO<inf>2</inf>
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Size-Dependent Graphene Support for Decorating Gold Nanoparticles as a Catalyst for Hydrogen Evolution Reaction with Machine Learning-Assisted Prediction
(2023-01-01)
Saeloo, Boontarika
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Jitapunkul, Kulpavee
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Iamprasertkun, Pawin
;
Panomsuwan, Gasidit
;
Sirisaksoontorn, Weekit
Size-dependent two-dimensional (2D) materials (e.g., graphene) have been recently used to improve their performance in various applications such as membrane filtration, energy storage, and electrocatalysts. It has also been demonstrated that 2D nanosheets can be one of the promising support materials for decorating nanoparticles (NPs). However, the optimum nanosheet size (lateral length and thickness) for supporting NPs has not yet been explored to enhance their catalytic performance. Herein, we elucidate the mechanism behind size-dependent graphene (GP) as a support due to which gold nanoparticles (AuNPs) are used as an active catalyst for the hydrogen evolution reaction (HER). Surprisingly, the decoration of AuNPs increased with the increasing nanosheet size, counter to what is widely reported in the literature (high surface area for smaller nanosheet size). We found that a large graphene nanosheet (lGP; ∼800 nm) used as the AuNP support (lGP/AuNPs) exhibited superior performance for the HER with long-term stability. The lGP/AuNPs with a suitable content of AuNPs provides a low overpotential and a small Tafel slope, being lower than that of other reported carbon-based HER electrocatalysts. This results from highly exposed active sites of well-dispersed AuNPs on lGP giving high conductivity. The laminar structure of the stacked graphene nanosheets and the high wettability of the lGP/AuNPs electrode surface also play crucial roles in enhancing electrolytes for penetration in the electrode, suggesting a highly electrochemical surface area. Moreover, machine learning (Random Forest) was also used to reveal the essential features of the advanced catalytic material design for catalyst-based applications.
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Preparation of Nanofibers of Poly (methyl methacrylate) Composited with Few-Layer-Graphene for Anticorrosion Layer
(2022-12-01)
Onlaor, Korakot
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Putta, Boonthawee
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Thiwawong, Thutiyaporn
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Tunhoo, Benchapol
An anticorrosion layer is a significant component that prevents the corrosion process in materials. In this work, a nanofiber of poly (methyl methacrylate) composited with few-layer-graphene was prepared as an anticorrosion layer. An electrospinning process was applied to prepare composite nanofiber on a metal substrate at various concentrations of few-layer graphene. The physical properties of the composite nanofiber were investigated with field-emission scanning electron microscope, Raman spectroscopy, and contact angle measurement. The corrosion behavior was tested in an aqueous solution of 3.5% by weight of sodium chloride. It was found that a few-layer graphene concentration of 2 wt% in polymethacrylate showed the optimum anticorrosion on aluminum sheet, as observed on a Tafel graph. Compared with the uncoated metal, the coated aluminum sheet was protected against corrosion with a protection efficiency of 99.33%. The prepared materials prevented the infiltration of water and solution ions into the metal plate.
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"freeing" Graphene from Its Substrate: Observing Intrinsic Velocity Saturation with Rapid Electrical Pulsing
(2016-01-13)
Ramamoorthy, H.
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Somphonsane, R.
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Radice, J.
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He, G.
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Kwan, C. P.
Rapid (nanosecond-scale) electrical pulsing is used to study drift-velocity saturation in graphene field-effect devices. In these experiments, high-field pulses are utilized to drive graphene"s carriers on time scales much faster than that on which energy loss to the underlying substrate can occur, thereby allowing the observation of the highest saturation velocities reported to date. In a dramatic departure from the behavior exhibited by conventional metals and semiconductors, as the electron or hole density is reduced toward the charge-neutrality point, the drift velocity is found to reach values comparable to the Fermi velocity itself. Corresponding current densities are as large as 109 A/cm2, similar to the values reported for carbon nanotubes and for graphene-on-diamond transistors. In essence, our approach of rapid pulsing allows us to "free" graphene from the deleterious influence of its substrate, revealing a pathway to achieve the superior electrical performance promised by this material. The usefulness of this approach is not merely limited to graphene but should extend also to a broad variety of two-dimensional semiconductors.

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